Charges have been filed against a man who impersonated a federal agent, calling himself "Officer Franklin" in a string of robberies across the South Side.

James Blackman, 46, of the 6400 block of South Morgan Street in the Englewood neighborhood, has been charged with armed robbery with a handgun, impersonating a police officer, aggravated robbery and aggravated kidnapping.

He was arrested after police issued an alert about four armed robberies in the 7700 block of South Colfax Avenue in the South Shore neighborhood, the 8100 block of South Paxton Avenue in South Chicago, the 7000 block of South Justine Street in Englewood and the 8700 block of South Harper Avenue in Gresham.

All the robberies occurred in September. Blackman allegedly posed as a federal agent to lure victims into his silver SUV.

In the latest robbery, on Sept. 30 on South Justine, Blackman pulled up in an SUV and told a 41-year-old man that he was a federal officer and was conducting a homicide investigation, according to Police News Affairs Officer John Mirabelli said. The man told the victim he was "Officer Franklin." Other victims have reported the suspect using the same name.

While the suspect did not display a gun, the robber demanded that the man get inside his SUV, police said. "He raised his voice in an aggressive manner to get inside his vehicle," said Mirabelli.

After the man got into the SUV, the suspect drove a short distance, Mirabelli said. After pulling over in the 8000 block of South Oakley Avenue, the suspect demanded cash and then fled. The victim was released unharmed, Mirabelli said.

In other robberies, the suspect displayed a silver semi-automatic handgun before robbing them, police said.